Fuel cell separator material and method for manufacturing said material

Abstract

A process for producing a separator material suitable for fuel cells, wherein the separator includes a pure titanium or a titanium alloy as a base material. The method comprises an application step and a heat treatment step. The application step is a step of applying a carbon black to a surface of the base material which has a carbon concentration, at a position located at a depth of 10 nm from an outermost surface, of 10 atom % or less. The heat treatment step subjects the base material, which has undergone the application step, to a heat treatment in a low-partial-oxygen-pressure atmosphere having a partial oxygen pressure of 0.0667 Pa or more and 25 Pa or less.

The invention claimed is: 
     
       1. A process for producing a separator material, the process comprising:
 applying carbon black to a surface of a base material comprising pure titanium or a titanium alloy and having a carbon concentration of 10 atom % or less at a position located at a depth of 10 nm from an outermost surface of the base material; and 
 subsequently subjecting the base material to a heat treatment in an atmosphere having a partial oxygen pressure of 0.0667 Pa or more and 25 Pa or less so that a layer which is not TiC is formed. 
 
     
     
       2. The process according to  claim 1 , further comprising:
 before the applying, subjecting the surface of the base material to a carbon concentration reduction treatment so that carbon concentration at the position located at the depth of 10 nm from the outermost surface is 10 atom % or less. 
 
     
     
       3. The process according to  claim 2 , wherein the carbon concentration reduction treatment is a pickling treatment of pickling the base material in an acidic aqueous solution comprising hydrofluoric acid. 
     
     
       4. The process according to  claim 1 , wherein the heat treatment is conducted at a partial oxygen pressure of 0.0667 Pa or more and 21 Pa or less and in a temperature range of 300 to 800° C. 
     
     
       5. A separator material, comprising:
 a base material comprising pure titanium or a titanium alloy, and 
 a mixture layer formed on a surface of the base material and comprising a mixture of carbon black and titanium oxide yielded by an oxidation of some or all of titanium atoms diffused outward from the base material, 
 wherein a mass ratio of the titanium oxide to the carbon black in a cross-sectional area of the mixture layer is from 1:9 to 8:2. 
 
     
     
       6. The process according to  claim 2 , wherein the heat treatment is conducted at a partial oxygen pressure of 0.0667 Pa or more and 21 Pa or less and in a temperature of 300 to 800° C. 
     
     
       7. The process according to  claim 3 , wherein the heat treatment is conducted at a partial oxygen pressure of 0.0667 Pa or more and 21 Pa or less and in a temperature of 300 to 800° C. 
     
     
       8. The separator material according to  claim 5 , further comprising:
 a layer of carbon black on the mixture layer. 
 
     
     
       9. The separator material according to  claim 5 , wherein the mixture layer does not comprise titanium carbide. 
     
     
       10. The process according to  claim 1 , wherein the heat treatment is performed at a partial oxygen pressure of 0.0667 Pa or more and 20 Pa or less and at a temperature of 500 to 750° C. 
     
     
       11. The process according to  claim 1 , wherein the heat treatment is performed at 500° C. for 30 minutes. 
     
     
       12. The process according to  claim 1 , wherein the heat treatment is performed at 700° C. for 1 to 2 minutes. 
     
     
       13. The process according to  claim 1 , wherein, after the heat treatment, a second heat treatment in air atmosphere is performed. 
     
     
       14. The process according to  claim 1 , wherein the carbon black is a powder having a particle diameter of 20 to 200 nm. 
     
     
       15. The process according to  claim 14 , wherein an amount of the carbon black powder applied to the surface of the base material is 1 to 50 μg/cm 2 . 
     
     
       16. The process according to  claim 14 , wherein an amount of the carbon black powder applied to the surface of the base material is 2 to 50 μg/cm 2 .